Thick plated metal interconnects can be used to provide low resistance pathways in integrated circuits. The interconnects may be employed for high current bussing and similar applications of power integrated circuits and other types of integrated circuits. The interconnects may be in the form of copper because of its low resistance.
Bonding directly to copper interconnects would enhance the performance of integrated circuits by eliminating the high parasitic series resistance associated with bond pads and standard multi-level VLSI metal systems. Typical bonding systems such as aluminum wedge and gold ball bonding, however, suffer reliability problems when bonded to copper due to voiding of aluminum in copper. Copper on copper bonds also suffer reliability problems.
To overcome such reliability problems, nickel plating has been used as a cap metalization system for thick plated copper interconnects. Although a nickel cap has been demonstrated to work reliably for large aluminum wedge bonding, its manufacturability is not standard and its environmental cleanup is costly, and it is not reliable for gold bonds.